Phosphine inhibition

ABSTRACT

A composition comprising phosphorus and a minor amount of at least one radical inhibitor selected from 4-(p-n-trophenyl-azo)-1-naphthol and mono and fused bi- and tri-cyclic compounds bearing at least a first and a second substituent, the first substituent being selected from hydroxy, mercapto, oxo, thioxo, the second substituent being selected from hydrogen, hydroxy and mercapto when the first substituent is hydroxy or mercapto and from oxo and thioxo, when the second substituent is oxo or thioxo, the second substituent being located on the same ring and ortho or para to the first substituent, other than anthraquinone or a substituted anthraquinone has reduced levels of phosphine emission. Munitions containing the composition as the charge are less susceptible to corrosion.

The present invention relates to inhibiting phosphine release fromphosphorus by use of certain radical compounds.

Phosphorus finds a wide variety of applications in industry, forinstance in matches, pyrotechnics and munitions and as an oxidationinhibitor in some plastics. Generally the red allotrope is favoured overthe white allotrope because of its greater stability in air and easierhandling characteristics. However, a major difficulty with redphosphorus is that, on storage, there is a gradual release of phosphinewhich is toxic by inhalation and which can, in turn, give rise todiphosphine which is spontaneously flammable in air. In pyrotechnics andmunitions, phosphine liberated by the red phosphorus charge may diffusethrough the device, even through elastomeric seals, and can give rise tocorrosion of essential working parts, presumably after it has beenoxidised to phosphoric acid and phosphates. Phosphine is also liberatedby white and black phosphorus.

It has now surprisingly been discovered that certain compounds, whenadmixed with phosphorus, will reduce the rate at which phosphine isliberated thus prolonging the shelf-life of munitions and other productscontaining phosphorus and reducing the hazards presented bymanufacturing processes involving phosphorus.

The compounds in question are quinonic compounds and sulphur analoguesthereof, which are mono- and fused bi- and tri-cyclic compounds bearingat least a first and second substituent, the first and secondsubstituents each being selected from oxo and thioxo, the secondsubstituent being located on the same ring and ortho or para to thefirst substituent, other than anthraquinone or a substitutedanthraquinone.

The quinonic compounds and their sulphur analogues defined above willhereafter be referred to as "radical inhibitors".

The radical inhibitors used in the present invention may bear furthersubstituents in additions to the first and second substituents definedabove. Suitably, any such further substituents are selected from nitro,halo, for instance chloro, and alkyl, for instance tertiary butyl,substituents.

Preferably the first and second substituents are the same and mostpreferably the first and second substituents are both oxo.

The fused bicyclic radical inhibitors comprise two fused aromatic ringsand the fused tri-cyclic radical inhibitors comprise three aromaticrings.

With tri-cyclic radical inhibitors it is prefered that the first andsecond substituents are both located on a ring fused to both the othertwo rings.

Particular examples of the mono- and fused bi- and tri-cyclic compoundsuseful in the invention are:

1,4-naphthaquinone

1,4-benzoquinone

phenanthraquinone

and chloranil(tetrachloro-1,4-benzoquinone)

Preferences within this list are in accordance with those stated above.The most preferred compounds, in terms of ability to diminish phosphineemission from red phosphorus, are 1,4-naphthaquinone and1,4-benzoquinone.

When used to inhibit phosphine emission from white phosphorus, theradical inhibitor is selected having regard to the solubility of theradical in water since white phosphorus is normally stored under water.

The present invention therefore provides a composition comprisingphosphorus, preferably red phosphorus, and a minor proportion of atleast one radical inhibitor as hereinbefore defined.

The amount of radical inhibitor incorporated in the phosphorus willdepend to a certain extent on the degree to which phosphine emissionmust be inhibited and especially on the degree to which the usefulproperties of phosphorus are diminished by inclusion of the radicalinhibitor. It could be envisaged that for certain applicationsrelatively large amounts of radical inhibitor could be tolerated,whereas for pyrotechnic and munitions applications based on a redphosphorus charge, the compositions should not contain less than 90% redphosphorus by weight based on the total weight of the composition. Forease of handling and to improve stability, red phosphorus as supplied(i.e., "ex-works") usually contains a small amount of water and/or oil.Typically about 1.25% w/w of a light mineral oil is added to improvestability. Binders, for instance polybutyral, may be included at, forexample about 5% w/w, as may other additives required to modify theproperties of the red phosphorus. Therefore, for pyrotechnics andmunitions uses, the practical upper limit on the proportion of radicalinhibitor is about 2% w/w in total.

The lower limit on the proportion of radical inhibitor included in thecomposition is determined primarily by the degree of inhibition ofphosphine release required. Even very low levels of radical inhibitorwill have an effect on phosphine release but, for practical purposes, itis likely that at least 0.5% w/w will be required to ensure acommercially significant reduction in the phosphine emission. Preferablythe radical inhibitor is incorporated at about 0.5 to 1.5% w/w, mostpreferably at about 1% w/w.

Compositions according to the present invention may be produced by anyconvenient mixing process.

The present invention therefore further provides a process for producinga composition comprising phosphorus, preferably red phosphorus and aminor proportion of a radical inhibitor as hereinbefore defined whichprocess comprises admixing the phosphorus and radical inhibitor.

The invention also provides a process for inhibiting the release ofphosphine by phosphorus, preferably red phosphorus which processcomprises admixing a minor proportion of a radical inhibitor ashereinbefore defined to the phosphorus.

In one embodiment of the invention a "dry" mixing process is used inwhich red phosphorus, optionally containing small amounts of waterand/or oil, in powder form is admixed with the radical inhibitor also inpowder form. Further additives may be incorporated into the redphosphorus before, during and/or after it is mixed with the radicalinhibitor.

In another embodiment of the invention a "wet" mixing process is used,In this method the red phosphorus and the radical inhibitor are mixed inthe presence of a suitable organic solvent. Conveniently the redphosphorus is mixed with a quantity of the organic solvent and asolution, suspension or slurry of the radical inhibitor in a furtherquantity of the same or another organic solvent is then admixed with thered phosphorus. Alternative "wet" mixing protocols will be readilyapparent to the skilled person. Other additives and binders may be addedto the red phosphorus before, during, and/or after mixing with theradical inhibitor. The red phosphorus used in this process may containsmall amounts of water and/or oil.

Once the mixing process is completed, the organic solvent may be removedby conventional methods.

Suitable organic solvents for use in the present invention arenon-flammable. In certain circumstances it may be convenient to selectan organic solvent in which the radical is soluble. A particularlyconvenient organic solvent is methylene chloride.

The emission of phosphine from red phosphorus may be further inhibitedby removal of substantially all water from the red phosphorus, forinstance by oven drying and a drying step may be incorporated in theprocesses described above. However the adverse effect of drying on thegeneral stability of red phosphorus and therefore in the precautionsrequired in handling it should be considered. The presence of a lightmineral oil also contributes to inhibition of phosphine emission and itmay be considered advantageous to add such an oil, for instance at about1.25% w/w if this is not already present in the ex-works red phosphorus.One suitable oil is Quindilla 19,BP.

In a further embodiment of the present invention there is provided apyrotechnic or munitions device comprising a charge which is acomposition according to the present invention.

Construction of such pyrotechnics and munitions is entirely conventionaland need not be described here. A composition according to the presentinvention may be used directly in place of the known phosphorus chargein such pyrotechnics and munitions.

Whilst emission of phosphine by compositions according to the presentinvention is inhibited by the presence of a radical inhibitor ashereinbefore defined it is recognised that there may be a residualemission of phosphine and that, on prolonged storage the effect of theradical inhibitor will eventually be swamped and phosphine emissionwill, thereafter, increase. In order further to prolong the shelf-lifeof pyrotechnics and munitions susceptible to corrosion as a result ofphosphine emission from the charge, it is preferred that the pyrotechnicor munitions device also comprises a component capable of adsorbingphosphine. Such a component may, for instance, be an activated carbonand is preferably a silverdoped, impregnated granular or fibrousactivated carbon. A preferred form of material is activated carboncloth. Such materials are known and readily available. One particularlypreferred such material is an impregnated activated carbon doped with upto about 10% w/w silver in the form of silver nitrate; the preferreddopant providing about 1% w/w silver as silver nitrate. The impregnatedactivated carbon may be placed in the same space as the composition ofthe present invention forming the charge in the device or in anotherregion of the device, for instance in the same space or compartment asbut preferably not in intimate contact with a component or components tobe protected from corrosion. Further details of such phosphine adsorbingmaterials may be obtained from Hall, P.G. et al., Carbon, 23(4), 353-371(1985).

The invention will now be illustrated by the following examples whichare not intended to limit the scope of the invention in any manner.

EXAMPLES EXAMPLE 1

"Wet" Mixing

An aliquot of red phosphorus was weighed out and binder(polyvinylbutyral) was added in sufficient quantity to form 5% w/w ofthe final composition. Sufficient methylene chloride to ensure efficientmixing was added. An appropriate quantity of the test additive wasdissolved or suspended in a further small quantity of methylene chlorideand the solution or suspension added to the red phosphorus and binderand mixed. The mixture was then dried under an air-jet blowing acrossthe surface of the liquid, the test composition being stirredperiodically until it became putty-like and then continuously until dry.Once dry, the mixture was sieved through a 4 mm mesh sieve and dried ina shallow dish, in a oven at 70° C. for 2 hours, and then cooled.

Ex-works and Oven Dried Red Phosphorus

Unoiled amorphous red phosphorus was obtained directly from theproduction line of Albright and Wilson. This material was used directly(ex-works condition), or after drying for 3-4 hours at 70° C. (ovendried condition).

Accelerated Ageing Tests

Samples each weighing 1 g and comprising 94% w/w red phosphorus(ex-works or oven dried), 5% binder (polyvinylbutyral) and 1% w/w testadditive prepared by the "wet" mix method were each placed into aflat-bottomed flask together with a phial containing 2 ml of distilledwater to ensure a high humidity (greater than 80% RH) once the flask hasbeen sealed. The flasks were stored at 50° C. for a period of 30 hours.The atmosphere above the samples was then analysed as follows:

A 10 ml gas syringe was used to extract a sample of the atmospherewithin a flask by insertion of a hypodermic needle through a suba-seal.The syringe was flushed three times after insertion into the flask, theplunger pulled back beyond the required volume and left for 5 min toequilibrate, then pushed to the mark. The syringe was left 2 mins beforeremoval and immediate injection into the inlet port of a Packard 437 gaschromatograph previously calibrated using a certified gas mixtureobtained from British Oxygen Company. The syringe was left for 30seconds before removal from the injection port. Results were plottedusing a Hewlett Packard HP3390A integrator.

The phosphine concentration in the atmosphere over each sample is shownin Table 1 where the results are given as normalised responses relativeto blanks consisting of 1 g red phosphorus (oven dried or ex-works)stored under the same conditions and assigned the arbitrary value of100.

                  TABLE 1                                                         ______________________________________                                                           Relative Response                                                               Oven                                                            Additive      Dried   Ex-Works                                         ______________________________________                                        Blank    none            100     100                                          Invention                                                                              1,4 naphthaquinone                                                                            --      0,1.3                                        "        p-benzoquinone  --      0.4,4,12.5                                   "        phenanthraquinone                                                                             --      15.5,25                                      "        chloranil       --      37.8,40                                      Reference                                                                              p-nitrophenol   --      26.7,44.4,38.8                               "        quinol           38     46                                           "        4-tert-butylcatechol                                                                           20     48.8                                         "        4-(p-nitrophenyl-azo)-1-                                                                      --      26.7,66.7,47.5                                        naphthol (Magneson II)                                               "        phenol          --      42.7,76.7,83.8                               "        Diethyldithiocarbamate                                                                        168     115                                                   (Sodium salt)                                                        "        Sodium dimethylthio-                                                                          200     88.5                                                  carbamate                                                            "        Ammonium tetramethyl                                                                          100     100                                                   dithiocarbamate                                                      "        resorcinol       45     100                                          "        m-cresol        --      73.3,82.2,81.3                               "        p-cresol        --      60,68.9,87.5                                 "        2 hydroxybiphenyl                                                                             --      60,55.6,72.5                                 "        3 dimethylamino-phenol                                                                        --      72,70,76.3                                   "        1-(2-pyridylazo)-2-                                                                           --      56,71.1,88.8                                          naphthol (PAN)                                                       "        4-(p-nitrophenyl-azo)-                                                                        --      64,90,80                                              resorcinol (Magneson)                                                "        4-(2-pyridylazo-)                                                                             --      61.1,64.4,56.3                                        resorcinol (sodium salt)                                                      (PAR)                                                                "        anthraquinone   --      108,120                                      Comparison                                                                             Ex-Works Material,                                                                            244                                                           no additive                                                          ______________________________________                                    

EXAMPLE 2

Using the methods of Example 1, combinations of radical inhibitors weretested as additives. Each additive was included in the phosphorus at 1%w/w. Flasks, prepared as in Example 1, were stored at 50° C. and theatmosphere was sampled as described in Example 1 at 30 hours. Theresults are presented in Table 2.

                  TABLE 2                                                         ______________________________________                                                 Phosphine Conc.                                                      Mixture  (30h)             Relative Response                                  ______________________________________                                        Blank    122,122     mean 122  100                                            +C       65,65                 53.3                                           +Q       65,35                 45.9,28.7                                      +C+Q     37,35                 30.3,28.7                                      Blank    107,126     mean 115.5                                                                              100                                            +C       42,44                 35.1,37.8                                      +Q       74,71                 53.5,60.9                                      +C+Q     52,53                 44.6,45.5                                      Blank    140,156     mean 148  100                                            +C       62,55                 41.9,37.8                                      +Q       75,83                 52.7,55.1                                      +C+Q     48,48                 32.4,32.4                                      Blank    114,142,150,152                                                                           mean 144.5                                                                              100                                            +4TBC    45,45,38,35           31:1,31:1,25:3,24:9                            +C       42,50,52,58           29.1,34.5,35.0,40.1                            +4TBC+C  24,24,28,28           15.5,15.5,19.4,19.4                            ______________________________________                                         4 TBC = 4tert butylecatechol                                                  C = Chloranil                                                                 Q = Quinol                                                               

EXAMPLE 3

Samples containing 5% binder and 1% 1,4-benzoquinone (A), 5% binder and1% 1,4-naphthaquinone (B), 5% binder only (C) and no additives (i.e.100% Ex-Works red phosphorus) (D) were prepared by the "wet" mix methodof Example 1 and placed in flat-bottomed flasks together with a phialcontaining 0.5 ml or distilled water. The flasks were sealed and storedat temperatures as indicated Table 3. The atmosphere above the samplewas analysed at intervals and the rate of phosphine generation (ppmhr⁻¹) at the 30 hour mark are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                  Mix                                                                 Temp (°C.)                                                                         A      B          C    D                                          ______________________________________                                        20          0.08   --         0.2  0.87                                                   0.05   0.53       0.13 0.84                                                   --     --         0.09 16.67                                      30          0.12   0.12       0.18 1.92                                                   0.06   0.09       0.23 3                                                      --     0.13       0.15 22.2                                       40          0.16   0.12       0.33 2.1                                                    0.1    0.25       0.25 4                                                      0.83   0.18       0.28 3.5                                        50          0.25   0.29       0.43 5                                                      0.1    0.25       0.33 8                                                      0.16   0.35       0.43 4.5                                        60          0.33   0.23       0.5  25                                                     0.5    0.45       1.88 10                                                     0.15   0.2        0.4  29.1                                       70          0.44   0.35       --   19.35                                                  0.1    0.45       0.39 40                                                     --     0.12       0.67 24.2                                       ______________________________________                                    

We claim:
 1. A composition characterised by phosphorus and a minoramount of at least one radical inhibitor selected from quinoniccompounds and sulphur analogues thereof, which are mono- fused bi-andtri-cyclic compounds bearing at least a first and a second substituent,the first and second substituents each being selected from oxo andthioxo, the second substituent being located on the same ring and orthoor para to the first substituent, other than anthraquinone or asubstituted anthraquinone.
 2. A composition according to claim 1characterised by red phosphorus.
 3. A composition according to claim 2,characterised by at least 90% by weight based on the total weight of thecomposition of red phosphorus.
 4. A composition according to claim 1characterised by from 0.5 to 2% by weight based on the total weight ofthe composition of the or each radical inhibitor.
 5. A compositionaccording claim 1 characterised in that the radical inhibitor bears oneor more further substituents, each selected from halo and alkylsubstituents.
 6. A composition according to claim 1 characterised inthat the radical inhibitor bears only a first and a second substituentas defined in claim
 1. 7. A composition according to claim 1characterised in that, in the radical inhibitor, the first and secondsubstituents are both oxo.
 8. A composition according to claim 1characterised in that the radical inhibitor is a bi-cyclic compound andthe first and second substituents are both located on a ring fused withone other, aromatic ring.
 9. A composition according to claim 1characterised in that the radical inhibitor is a tri-cyclic compound andthe first and second substituents are both located on a ring fused withboth of two other aromatic rings.
 10. A process for producing acomposition comprising phosphorus and a radical inhibitor as defined inclaim 1, comprising admixing phosphorus and the radical inhibitor.
 11. Aprocess according to claim 10 characterised by admixing red phosphorusand the radical inhibitor in the presence of a suitable organic solvent.12. A process according to claim 11 characterised in that the organicsolvent is methylene chloride.
 13. A pyrotechnic or munitions devicecomprising, as the charge, a composition according to claim
 1. 14. Apyrotechnic or munitions device according to claim 13 and susceptible tocorrosion characterised by, in the same space as the charge, aphosphine-adsorbing component.
 15. A pyrotechnic or munitions deviceaccording to claim 13 and comprising a component susceptible tocorrosion, having a phosphine-adsorbing component in a space containingthat component.
 16. A pyrotechnic or munitions device according to claim14 characterised in that the phosphine-adsorbing component is activatedcarbon.
 17. A device according to claim 16 characterised in that theactivated carbon is doped with silver nitrate.